Different types of analog-to-digital converters (ADCs) can convert an analog signal into a digital signal. For example, a continuous-time delta sigma (CTDSM) ADC uses a delta-sigma modulator to convert an analog signal to a digital signal. The CTDSM ADC may use a loop filter to move low frequency quantization noise up to higher frequencies outside the band of interest. The out-of-band noise may then be filtered out, which may improve the analog-to-digital conversion dynamic range.
A quantizer in the delta-sigma modulator may receive the output of the loop filter and perform the analog-to-digital conversion to output a digital signal. A feedback loop of the CTDSM ADC includes digital-to-analog converters (DACs) that convert the digital output of the quantizer to corresponding analog values. The analog values are then subtracted from the input signal of the loop filter or internal nodes within the loop filter, and the resulting signal is input back into the loop filter and then the quantizer.
Continuous-time delta-sigma ADCs may suffer from excess loop delay (ELD). Excess loop delay may be caused by a finite propagation delay between the time the quantizer samples the analog signal and the time that the feedback DACs present analog versions of the quantized samples back to the loop filter. The excess loop delay may degrade the stability of the CTDSM ADC and should be compensated for. For example, the CTDSM ADC may add an independent signal path, such as an excess loop delay compensation feedback path to compensate for the excess loop delay.